Abstract: Introduction: Polylactic acid is one of the pioneer biodegradable polymers. It is produced by fermentation of bio based starch sources such as maize, wheat and potato and polycondensation of the lactic acid [1]. Among numerous bioplastics, poly(lactic acid) (PLA) is considered the most promising and popular biobased material because of its ideal properties in use: low weight, low processing temperature (compared to synthetic polymer), no environmental pollution, good printability, high degree of transparency, and ease of conversion into different forms. PLA has many applications. It provides potential use in plastic applications, packaging, agricultural products, disposable products, and the medical field [3]. Among the biodegradable polymers, PLA plays an important role because of its excellent mechanical properties. On the other hand, PLA has some drawbacks such as low toughness, low thermal stability and poor processability [3]. These drawbacks can be accomplished by the usage of plasticizers or different types polymers. Polyethylene glycol (PEG) is one of the widely used plasticizers for PLA [4]. In addition, easy flammability properties of PLA restrict its use in electric and electronic industries. It can be improved by flame retardants addition. [5] In addition, the silica and carbon-containing rice husk ash (RHA) has potential to improve the flame retardant property, mechanical strength and thermal stability of PLA. RHA is used in building material as building insulation and mineral source for concrete. [6] Considering the mechanical properties of RHA, the mechanical property of PLA can be improved with PLA/RHA mixture. Goal: It is aimed to evaluate the RHA effects on the flame retardant properties of PLA based composites. Also, it is studied to decrease ammonium polyphosphate (APP) usage with the addition of increasing content RHA in the PLA / PEG / APP composite to enhance the flame retardant properties. Method: Poly (lactic acid) was plasticized with PEG and it used as the matrix material of the composites. APP, pentaerythritol (PER) and RHA were selected as intumescent flame retardant systems. While the APP/PER ratio decreased, RHA ratio was increased. Loading levels of RHA were changed as 3 wt.%, 5 wt.% and 10 wt.%. All compositions were mixed in a laboratory scale extruder at 200 °C for 3 min. mixing time and 100 rpm mixing rate. Then, the polymeric melt was molded using a laboratory-scale injection molding machine with a pressure of 10 bar and a mold temperature of 25 °C. Discussion: Characterization of the composites were performed by differential scanning calorimetry (DSC), tensile test, thermogravimetric analysis (TGA), limiting oxygen index (LOI). Results: The highest crystallization degree and Tg value were obtained PLA/PEG/APP/PER/3RHA blend as 17.56 % and 53.2°C, respectively. 5 wt.% RHA addition decreased the crystallization degree of the sample. Also, the crystallization degree of the prepared composites decreased with increasing RHA content. While the melting temperature of the composites did not change, glass transition temperature decreased approximately 5 °C. It was seen that the decomposition starting temperatures of all composites are above 200 ºC. For this reason, it can be said that the produced nanocomposites did not deteriorate during production process at the production temperature of 200 ºC. Besides, it was seen no residue in TGA for all of the composites at 600 oC. While the addition RHA to the PLA increased LOI value of neat PLA, enhancing RHA content decreased LOI values of the composites. Generally, the strain at break values of the composites was decreased with the increasing loading level of the RHA. The maximum tensile strength value among the RHA including composites was obtained for the 3 wt.% RHA reinforced PLA based composites as 34.2 MPa.
Anahtar Kelimeler: Biodegradable polymer, Poly(lactic acid) (PLA), Rice husk ash (RHA)
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